Furin is a protein processing enzyme of the family of proprotein convertases (PCs), which has a significant role in cancer etiopathogenesis. In this application, we propose to investigate the function of furin during skin tumor development, focusing on the early and late changes that take place after UV exposure of the mouse skin. PACE4, another related PC, has been shown to have a role in murine tumor cell invasiveness by activating relevant proteases. Furin is also able to enhance cell proliferation in human precancerous and cancer cells by activating growth factor and growth factor receptors, such as IGF-R1. The lack of a mouse model to study the function of furin during carcinogenesis prompted us to design a series of experiments using transgenic mice to facilitate the better understanding of this prominent PC in the etiopathogenesis of skin cancer. Our objective in this proposal is to determine the mechanisms by which furin contributes to tumor development alone or in combination with PACE4 using transgenic mice overexpressing PCs. Two aims have been designed to this effect: First we will determine if the targeted in vivo overexpression of furin alone will enhance the development of experimental skin cancer induced by UV. We shall investigate the simultaneous in vivo overexpression of PACE4 and furin using bigenic mice in order to establish the possible cooperation of the 2 PCs in skin carcinogenesis. Substrate- specificity will be evaluated in keratinocyte cultures derived from monogenic (K5-PACE4 and K5-Furin) as well as from bigenic mice (K5-PACE4/Furin). These experiments will clarify the significance of furin's pro-proliferative effect and whether its pro-invasive effects are the same or different from PACE4's predominant pro-invasive function. In addition, this specific aim will determine whether the combination of both PCs have an enhancing effect on any or both of these biological processes. Second, we will also determine if PC inhibition blocks tumor growth and development in transgenic models. Crossing monogenic PC transgenic mice as well as double transgenics K5-Furin/PACE4 with K5-PDX and K5-PC-Propeptide transgenic mice expressing either the cDNA of a competitive PC peptide inhibitor or that of the physiological inhibitors of PCs, we will determine if inhibition of PCs alters the formation of skin tumors induced by UV carcinogenesis. PUBLIC HEALTH RELEVANCE: This application will use modern experimental animal models to dissect the function of proprotein convertases, enzymes that activate relevant cancer-associated biomolecules, during the early formation and growth of squamous cell carcinomas, one of the most common cancers of the human skin. The proposed studies will lead to the identification of mechanisms involved in the origination of cancer that could be of great practical value in its early diagnosis and treatment.